Potentiometer applications include a wide variety of electronic devices and uses within the devices. Potentiometers are commonly used to provide input from sensors and controls, by achieving a defined relationship between a mechanical position and a variable resistance. An electronic measurement system monitors the dependent resistance characteristic of the potentiometer to determine the mechanical position, and subsequently an output voltage related to the position of the device is determined. One example application of a potentiometer is an adjustment dial for a user interface to an electronic motor overload relay.
These electronic systems depend on defined performance characteristics of the potentiometer. Potentiometer manufacturers define performance variations over various criteria, such as application temperature or the vibration environment. However, eventually all potentiometers succumb to some wear out and fail. When the potentiometer fails, the electronic system no longer receives the input that was controlled or monitored through the potentiometer. This can correspond to a loss of functionality in the device using the potentiometer because of the loss of electrical input from the monitored sensors or controls.
Today, multiple approaches exist to address the eventual wear out and resulting failure of the potentiometer. One approach uses analysis and testing to demonstrate that the potentiometer will not fail over the service life of the device. In this case, the failure is not actively detected or mitigated in the application, however the robustness of the potentiometer is deemed adequate to avoid a loss of functionality in the device. Another approach uses detection means to determine when the potentiometer has failed, and to take some subsequent action. The action may include alerting the user, or entering a safe state such as shutting down the device.
Prior methods of detecting potentiometer failure exist. However the known methods involve overhead and cost, including the need for additional physical components, which are not suitable for all applications. Known methods also include monitoring characteristics of the potentiometer, which may be important in some applications, but not important in others. An example application with constraints on component cost that is impacted by specific failure modes of the potentiometer is an electronic motor overload relay.
In such an electronic motor overload relay, a potentiometer may be used as a voltage divider, where the divided voltage is determined by the position of an adjustment dial for a user interface to set the motor full load current parameter for the device. When the potentiometer is used as a voltage divider in this application, changes in some parameters of the potentiometer during the motor life such as change in the resistance value over temperature, do not affect the performance of the potentiometer in the device. However, a failure in which any connection within the potentiometer becomes open circuit, either between mechanical interfaces of the potentiometer subcomponents or between the potentiometer and the electronic board, can affect the performance of the device.
Thus, a need exists for a potentiometer failure detection system that reliably detects the failure of a potentiometer. There is a further need for a system that uses components for the reading of a potentiometer to determine failures. There is also a need for a detection system that can identify the specific source of the failure for the device in which it is permissible or preferred to continue operating in the presence of certain distinguishable potentiometer failures.